Electric incandescent lamp



Aug. 22, 1961 W. F. HODG E ELECTRIC INCANDESCENT LAMP Filed Jan. 2, 1958lnventov: WiLLiam F l-lod cgga, b WW;

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United States Patent 2,997,617 ELECTRIC INCANDESCENT LAMP William F.Hodge, Lyndhurst, Ohio, assignor to General Electric Company, acorporation of New York Filed Jan. 2, 1958, Ser. No. 706,828 3 Claims.(Cl. 313-278) My invention relates to electric incandescent lamps orsimilar devices comprising a sealed envelope containing an incandesciblefilament for emission of radiant energy. More particularly, theinvention relates to lamps having an elongated envelope containing astraight wire filament which is required to be maintained taut duringoperation.

The use of long filaments of straight tungsten wire, which expand andsag under their own weight upon being heated to incandescence, requiresthe provision of means which will maintain the filament taut under allconditions and, at the same time, will permit of ready expansion andcontraction of the filament without subjecting it to undue strains. Itis an object of this invention to provide a unique and especiallyadvantageous, inexpensive and reliable spring tension means forperforming that function.

Further objects and advantages of my invention will appear from thefollowing description of a species thereof and from the drawing wherein:

FIG. 1 is a side view, partly in section, of a lamp embodying theinvention; and

FIG. 2 is a fragmentary perspective as viewed from the line 2-2 in FIG.1 and showing the connection of the filament to the tensioning springmeans.

Referring to the drawing, the lamp illustrated therein comprises anelongated tubular envelope 1 of glass or quartz preferably containing afilling of inert gas, such as argon at a pressure of several hundredmillimeters. The envelope is sealed at both ends of compressed orflattened pinch seal portions 2 in which are embedded portions oflead-in or current supply conductors 3. When the envelope 1 is ofquartz, the conductors 3 preferably consist of wires of molydenum havingextremely thin intermediate flattened or foliated portions 4hermetically sealed in the seal portions 2. The envelope 1 also containsan incandescible filament 5, preferably of straight tungsten wire, whichis fixedly secured as by welding, at one end to the inner end of thelead-in conductor 3 at the left in FIG. 1.

In accordance with the invention, there is provided at the opposite orright hand end of the lamp a spring tension means comprising a wirehelix 6 preferably of tungsten. The diameter of the helix 6 is a littleless than the inside diameter of the envelope 1, allowing it to slidefreely therein. One end of the helix 6 is secured, as by welding, to theadjacent lead-in conductor 3. The other, or remote, end of the helix 6rests against a retaining means which is fixed relative to the envelope1 and which is here illustrated as a pair of opposed inwardprotuberauces 7 formed by indentations or constructions in the wall ofthe envelope.

The right hand end of the filament is supported from a point on thehelix 6 intermediate its ends. As herein illustrated, the end of thefilament is welded directly to a part of one of the turns of the helixwhich has been distorted, as shown at 8, to bring it substantiallyacross the axis of the envelope 1. During assembly of the lamp, the seal2 at the right is made first. The lead-in conductor 3 at the left,previously welded to the filament, is then pulled down into sealingposition to thereby compress the part 9 of the helix against theprotuberances 7. Suflicient compression is introduced to make sure thatexpansion of the filament, when heated to incandescence, will be takenup by the spring action of the part 9 with suflicient residual tensionto keep the filament taut.

During operation of the lamp, current flows through the part 10 of thehelix to the filament 5. The wire sizes employed for the helix 6 andfilament 5 are so proportioned that the design current necessary to heatthe filament to desired operating temperature will heat the part 10 ofthe helix to a red heat. At this temperature the helix portion 10 isrelatively soft and acts as aflexible current conductor. However, thespring portion 9 of the helix does not carry current and, therefore, itis not softened and maintains the necessary tension on the filament tokeep it straight.

In a specific lamp designed for infrared radiation, the envelope 1 maybe of quartz tubing having an inside diameter of 7.75 mm., the filament5 may be a tungsten wire of .013 inch diameter and 11% inch overalllength, to operate at a color temperature of approximately 3400" K. at acurrent of about 14.05 amperes from a source of 52.5 volts across thelamp terminals, and the helix 6 may be of tungsten wire of about .019inch diameter with the portion 10 heated to a red heat during passage ofthe current therethrough.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric incandescent lamp comprising a sealed tubular envelope, apair of current supply conductors sealed in opposite ends of saidenvelope and extending thereinto, a helical compression spring ofslightly smaller diameter than said envelope located adjacent one end ofthe envelope, retaining means fixed relative to the envelope and engagedby the end of said spring remote from said one end of the envelope, astraight wire incandescible filament securely connected at one end tothe current supply conductor at the other end of the envelope, saidfilament extending longitudinally of the envelope and into the interiorof said spring and supported at its other end from a part of said springspaced from its said remote end, the spring being held, by said filamentagainst said retaining means under compression suflicient to take up theexpansion of the filament when heated to incandescence and maintain thefilament taut, and flexible conductor means electrically connecting thesaid other end of the filament with-the current supply conductor at thesaid one end of the envelope.

2. An electric incandescent lamp comprising a sealed tubular envelope, apair of current supply conductors sealed in opposite ends of saidenvelope and extending thereinto, a helical compression spring ofslightly smaller diameter than said envelope located at one end of theenvelope and having a proximate end secured to the current supplyconductor at said end of the envelope, retaining means engaged by theremote end of said spring and fixed relative to said envelope, astraight wire incandescible filament securely connected at one end tothe current supply conductor at the other end of the envelope, saidfilament extending longitudinally of the envelope and into the interiorof the said remote end of said spring and supported at its other endfrom and electrically connected to a part of said spring intermediatethe ends of the spring, the portion of said spring between saidretaining means and the part secured to said other end of the filamentbeing under compression suflicient to take up the expansion of thefilament when heated to incandescence and maintain the filament taut,the remainder portion of said spring serving as a flexible currentsupply conductor.

3. An electric incandescent lamp comprising a sealed tubular envelope, apair of current supply conductors sealed in opposite ends of saidenvelope and extending thereinto, a helical compression spring ofslightly smaller diameter than said envelope located at one end of theenvelope and having a proximate end secured to the current supplyconductor at said end of the envelope, retaining means engaged by theremote end of said spring and 3 fixed relative to said envelope, astraight Wire incandescible filament securely connected at one end tothe current supply conductor at the other end of the envelope, saidfilament extending longitudinally of the envelope and into the interiorof the said remote end of said spring and supported at its other endfrom and electrically connected to a part of said spring intermediatethe ends of the spring, the portion of said spring between saidretaining means and the part secured to said other end of the filamentbeing under compression sufficient to take up the expansion of thefilament when heated to incandescence and maintain the filament taut,the remainder portion of said spring serving as a flexible currentsupply conductor and being proportioned relative to said filament sothat the design current necessary to heat said filament to its 152,731,579

normal operating temperature will heat said remainder portion of thespring to a red heat and thereby minimize the tension therein.

References Cited in the file of this patent UNITED STATES PATENTS1,745,181 Mischler Jan. 28, 1930 1,975,499 Braselton Oct. 24, 19342,078,360 Ziegenbein Apr. 27, 1937 2,342,044 Foote Feb. 15, 19442,521,315 Victoreen Sept. 5, 1950 2,521,682 Backer etal Sept. 12, 19502,523,033 Leighton Sept. 19, 1950 2,532,956 Simpson Dec. 5, 1950 WeissJan. 17, 1956

